Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $125.98   8.434%   $136.6052   $136.61   $136.60   $136.60  
  Purchase #2 $165.72   6.614%   $176.6807   $176.68   $176.70   $176.70  
  Purchase #3 $38.68   11.206%   $43.0145   $43.01   $43.00   $43.00  
  Purchase #4 $64.81   13.322%   $73.444   $73.44   $73.45   $73.40  
  Purchase #5 $219.76   8.330%   $238.066   $238.07   $238.05   $238.10  
  Purchase #6 $89.91   3.332%   $92.9058   $92.91   $92.90   $92.90  
  Purchase #7 $41.26   7.477%   $44.345   $44.35   $44.35   $44.30  
  7 purchase totals = $746.12       $805.0612   $805.07   $805.05   $805.00